This invention relates to the mass simultaneous sealing and electrical connection of electronic devices. Note particularly, the invention relates to a new and economically efficient method of making relatively inexpensive hermetically sealed packages for surface acoustic wave devices.
Many electronic devices are very sensitive and need to be protected from harsh external ities, including various potentially damaging contaminants, present in the environment. Heretic packages have proven to be a very effective means for providing such protection. The seal of a heretic package is an airtight one. Known heretic packages have been made from metal, glass, or ceramic, and a means of sealing, such as solder or welding. Nonhermetic structures have also been used for affording a degree of protection to electronic devices not requiring a complete isolation from the environment. Known nonhermetic packages have employed plastic encapsulation, molding, potting, or polymer sealing. In the past, a trade-off has been required between using heretic packages, which have afforded a maximum degree of protection at a higher cost, and using nonhermetic packaging, which has offered less protection at a lower cost. The reason for the high cost of heretic packages will become apparent from the exemplary description of a prior method of making such structures, which is set forth next.
Customarily, the individual electronic devices to be sealed are initially constructed. The electronic devices are then mounted inside of a package which is suitable for hermetic sealing, typically made of metal and glass or ceramic components as stated above. Next, conductive wire or ribbon bonding is performed between electrical terminals located inside of the package and terminals of the electrical device itself. Such connections enable each electronic device to electrically communicate with a region outside of the package. Subsequently, the package is sealed by metal bonding techniques, such as projection welding or seam sealing. Finally, each individual package and part are electrically tested to determined electrical specifications. Such testing is necessary since the various steps carried out during production usually causes the yield of each unit to drop below one hundred percent. These steps for hermetic packaging and electrical testing have commonly been carried out individually (i.e., one by one) for each electronic device.
The combined cost of the labor to carry out these operations for an individual electronic device together with the cost of the packaging oftentimes far exceeds the cost of the electronic device itself. There has long existed, therefore, a recognized need for a less expensive method for hermetically sealing electronic devices from the external environment; and also, a need for being able to electrically test them in an economically efficient manner. Additionally, due to the complexity of the assembly, such operations have lead to a device which can be undesirably large in size.
One example of an electronic device which is preferably hermetically packaged for use due to its sensitive nature, and which has been commonly packaged in a manner such as that set forth above, is a surface acoustic wave (SAW) device. SAW devices are well known in the art and are extremely useful in a number of different applications, including highly accurate and stable band pass filters and oscillators operating from tens of MHz to beyond 1 GHz.
Environmental contaminants can cause SAW devices to seriously malfunction, often to the point that they are rendered useless for their intended purpose. For example, contamination of a SAW device can change the acoustic wave propagation velocity and increase attenuation through the SAW substrate. For SAW devices, any change in velocity results in frequency shift, and an increase in attenuation results in increasing insertion loss. Thus, hermetic packaging for each individual SAW device has routinely been utilized in order to ensure that the surface of each device is kept free of contaminants that could reflect or otherwise interfere with propagating surface acoustic wave energy.
As stated above, however, the known methods for hermetically encapsulating electronic devices (such as SAW devices) have proven expensive and can result in the production of units which are often undesirably large in size.
It is, therefore, a primary object of the present invention to provide a new and effective method for the sealing and electrical testing of electronic devices; and particularly for surface acoustic wave devices.
It is also an object of the invention to provide a highly cost efficient method capable of producing either a hermetic package or a nonhermetic package, whichever is desired in a particular instance, for an electronic device.
It is additionally an object of the invention to provide a method for producing a surface mount compatible device which is compact in size.